The present invention generally relates to methods and apparatus for cleaning components, more particularly, to methods and apparatus for cleaning gas turbine combustors.
A combustor is an important component of a gas turbine engine. Combustors comprise a combustion chamber defined by one or more combustor liners and a combustor dome. One of the more common combustor configuration types used in gas turbine engines, such as auxiliary power units (APU), is an annular combustor. An inner liner, an outer liner and a dome define the combustion chamber of an annular combustor. A mixture of fuel and air is introduced into the combustion chamber where it is ignited to produce combustion gases for a downstream turbine.
Because combustors are exposed to the temperatures generated by hot combustion gases (commonly in excess of 3500° F.) and the materials used in combustor construction are limited to about 1700-1800° F., cooling must be provided to the combustor components. A widely used technique for protecting combustor liners from hot combustion gases involves covering the combustor liners with a matrix of small holes, usually about 0.015 to 0.030 inches in diameter (effusion holes). A supply of cooling air is passed through the effusion holes to cool the liners and to add airflow to the combustion gases.
During the normal operation of the gas turbine engine, environmental contaminants can accumulate on the surfaces of the combustor, reducing engine efficiency. Additionally, contaminants can gather in the effusion cooling holes, the subsequent effusion hole plugging restricts airflow into the combustor, reducing the lean blowout margin until the gas turbine engine has little or no margin, resulting in uncommanded shutdowns of the gas turbine engine. Contaminant deposits in the effusion holes can also reduce liner cooling efficiency. Methods for removing contaminant deposits from engine components have been described.
Solid particle abrasives comprising nutshells, coke, molybdenum and/or graphite particles have been used to clean components. In these methods, the particles impinge on the surfaces of the component to dislodge deposit buildup. These techniques have been useful in removing deposits in some applications. Unfortunately, the abrasive particles can damage the base alloy and may become lodged in cracks or effusion holes during the cleaning process. Additionally, some engine components include internal passageways, such as effusion holes, which may not be sufficiently cleaned using these methods.
A component cleaning process that does not require the use of abrasive particles is disclosed in U.S. Patent Application No. 2002/0103093. In the described method, an engine component is immersed in an acid solution bath. The bath is agitated to aid in component cleaning. Although this method may remove contaminant buildup from effusion holes, it requires the component to be removed from the engine and immersed in the solution. For some applications, component removal is a time consuming and costly process.
Another cleaning process is disclosed in Japanese Patent Publication No. 2001214755. In the disclosed method, a nozzle is mounted to the combustor plenum and used to spray a cleaning fluid onto the outer surface of a combustor liner. Although this method may be useful for cleaning some combustors, it may not be suitable for cleaning all combustor configuration types. For example, the described method may not provide sufficient cleaning to the inner liner of an annular combustor because the cleaning fluid may not adequately contact the surfaces of the inner liner.
As can be seen, there is a need for improved component cleaning methods. Further, a cleaning method is needed that does not require the use of abrasive particles or the removal of the component. A method of removing contaminant deposits from combustor effusion holes is needed that does not require combustor removal.